A wind turbine known in the art comprises a tapered wind turbine tower and a wind turbine nacelle positioned on top of the tower. A wind turbine rotor with a number of wind turbine blades is connected to the nacelle through a low speed shaft, which extends out of the nacelle front as illustrated on FIG. 1.
When conducting current through a conductor the conductors temperature is raised. When the temperature is raised the conductor expands and particularly the conductors length will be increased. When the temperature drops again, the conductor contracts accordingly.
If the conductor is a cable comprising a number of twisted conductors, the “windings” of the conductors to some degree will be able to absorb this motion, but if the cable is a solid core conductor of a substantial diameter, this movement of the cable can be very forceful and therefore potentially very damaging.
If a conductor connects two fixed electrical components, this extension and contraction of the cable can either lead to the cable bending or applying considerable strain to the components. This is of course disadvantageous, in that it can damage the cables insulation, it can damage the components or otherwise create undesired scenarios, which might lead to short circuits or other kinds of damage.
For instance a wind turbine is provided with one or more generators to transform the energy of the wind to electrical current. A wind turbine generator known in the art among other things comprise a rotor and a stator. E.g. through a gear the wind turbine blades are connected to the rotor in the generator. When the blades rotate the rotor is thereby also rotated and high current electricity is produced.
To lead the current from the electromagnets of the rotor, the rotor shaft is provided with a number of slip rings, which are connect to their respective rotor coils by a number of relatively thick solid core conductors. These conductors are usually made as solid rods with a diameter of up to 10 mm or more, and they are typically made of copper or another material with excellent current conducting qualities. The rotor shaft on the other hand is usually made of steel, making it able to withstand the large loads it is exposed to.
The coefficient of expansion of the conductors is therefore usually larger than the shafts coefficient of expansion and e.g. due to loss, the conductors becomes very hot during use. This means that the conductors extend and contracts more than the shaft, which will lead to relative motion between the cables and the shaft or other fixed neighbouring components, which do not extend correspondingly.
This relative motion is very disadvantageous, in that the cables insulation might be damaged due to rubbing or the cables might break lose, which in worst case can lead to short circuits, which can be very damaging to the cables, the generator or other components.
An object of the invention is therefore to provide for a technique for handling the extension and contraction of high current conductors, thereby reducing the risk of damage to the conductors or other components.
Especially it is an object of the invention to provide technique for handling the extension and contraction of high current conductors in a wind turbine.